Doctor of Philosophy
Centre for Medical Radiation Physics - Faculty of Engineering
Hardcastle, Nicholas, Towards optimal treatment planning and novel dosimetry for cancer patients receiving intensity modulated radiation therapy, Doctor of Philosophy thesis, Centre for Medical Radiation Physics - Faculty of Engineering, University of Wollongong, 2009. http://ro.uow.edu.au/theses/3068
Modern radiation oncology is constantly improving and becoming more complex. Novel dosimetric planning, delivery and dosimetry techniques have allowed for im- proved plan quality and confidence in delivery. This thesis is an investigation into the impacts of novel radiotherapy planning and delivery techniques and the efficacy of novel dosimetry methods for modern, complex radiotherapy. The first part of the thesis involved investigation into novel treatment planning optimisation techniques for prostate cancer radiotherapy. Advantages and disadvantages of IMRT for simple prostate radiotherapy in the Australian clinical setting is investigated, showing small gains compared with high quality conformal radiotherapy. The use of a radiobiological parameter, specifcally the generalised Equivalent Uniform Dose (gEUD) was investigated for prostate IMRT optimisation to reduce rectal dose. The gEUD metric was found to be a useful optimisation objective that provided rectal dose reductions over the full dose range. The result of the optimisation was heavily dependent on the value of a (describing organ architecture), with a lower value of a resulting in the largest reductions in rectal dose. A commercial Volumetric Modulated Arc Radiotherapy (VMAT) tool was investigated for prostate radiotherapy. Single arc VMAT plans were compared to static gantry angle IMRT plans for prostate cancer cases. It was found that VMAT resulted in equivalent target coverage with reductions in rectal V25Gy. The VMAT plans required on average 18.6% fewer monitor units and were theoretically up to 3.75 times faster to delivery compared with static gantry angle IMRT. The second part of the thesis looked at using modern radiation detectors for verification of treatment dose in regions of electronic disequilibrium. Rectal balloons filled with air are used for prostate immobilisation and rectal dose reduction in prostate photon radiotherapy. This introduces an air cavity into the patient, immediately adjacent to the target. Radiochromic film was used to show that two commercial convolution/superposition dose calculation algorithms slightly over-predict the anterior rectal wall dose and under-predict the posterior rectal wall dose. The feasibility of a novel MOSFET detector, the MOSkin, coupled to a commercial rectal balloon was investigated for real time in vivo rectal wall dose verification. In this phantom study, the MOSkin was shown to be an excellent real time dosimeter, with minimal angular response and reproducible sensitivity. The MOSkin was then used with radiochromic film to verify the dose delivered to the skin during total scalp irradiation with helical tomotherapy. It was shown that the helical tomotherapy RTPS accurately calculated the dose to surface voxels and that the dose delivered to the skin is less than the prescription dose, which suggests a bolus may be required to achieve prescription dose to the skin. Finally, the dosimetric effect of end leaf leakage was investigated for a commercial multileaf collimator for wide-field IMRT. It was shown that end leaf leak- age can contribute significant doses to treatment fields, but provided the effects are quantified it is reasonable to accept these as the allowance of wide fields avoids complicated dual overlapping field feathering. The commercial RTPS investigated slightly under-predicts the magnitude of these end leaf leakage dose contributions.
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